HOURLY pay for union building trades workers averages $6.39 in cities of 100,000 or more, up 11.9% from January 1970. Including fringe benefits, employers' costs run 13% higher, or $7.23 an hour. As usual, the Labor Department's latest wage figures show wide variations among trades and cities. Examples:
CITY ELECTRICIANS PLUMBERS CARPENTERS LABORERS
Atlanta $7.15 $6.85 $6.65 $3.85
Chicago 7.80 6.90 6.85 5.40
Cleveland 8.03 8.35 8.10 6.52
El Paso 5.60 5.50 4.72 2.71
Nashville...